Fix Travis CI build (php7.2 with coverage=1 lint=1 stage)

[baspeeters]

This PR fixes the failing Travis CI build stage. Running builds that have succeeded in the past cause them to fail when ran again. The problem consisted of 2 parts (kept 2 commits because different tickets, but same purpose of fixing build 🤷‍♂️).

Problem 1: A namespacing error (#166)

Example build: https://travis-ci.org/api-platform/schema-generator/jobs/541147735

The dependencies aren't locked down very strict and a composer update was done before this travis stage was ran. This caused the dependencies for this stage to be updated beyond the lock file. Changing the command from update to install solved this.

Problem 2: Whitespace in e2e test files (#167)

Because of problem 1, the compile script never reached the point where it tests to diff against the produced files in tests/e2e/. Because the tests had been failing for some time, something changed which makes the files not match with the produced files anymore (but it's only a space):

[warning] The property "address" (type "Person") has several types. Using the first one ("PostalAddress") or possible options("PostalAddress", "Text").
+ diff tests/e2e/src/AppBundle/Entity/Person.php tmp/AppBundle/Entity/Person.php
34c34
<      * @ORM\Column(type="text", nullable=true)
---
>      * @ORM\Column(type="text",nullable=true)
42c42
<      * @ORM\Column(type="text", nullable=true)
---
>      * @ORM\Column(type="text",nullable=true)
50c50
<      * @ORM\Column(type="text", nullable=true)
---
>      * @ORM\Column(type="text",nullable=true)
58c58
<      * @ORM\Column(type="text", nullable=true)
---
>      * @ORM\Column(type="text",nullable=true)
74c74
<      * @ORM\Column(type="date", nullable=true)
---
>      * @ORM\Column(type="date",nullable=true)
83c83
<      * @ORM\Column(type="text", nullable=true)
---
>      * @ORM\Column(type="text",nullable=true)
91c91
<      * @ORM\Column(type="text", nullable=true)
---
>      * @ORM\Column(type="text",nullable=true)
100c100
<      * @ORM\Column(type="text", nullable=true)
---
>      * @ORM\Column(type="text",nullable=true)
109c109
<      * @ORM\Column(type="text", nullable=true)
---
>      * @ORM\Column(type="text",nullable=true)

Q	A
Bug fix?	yes
New feature?	no
BC breaks?	no
Deprecations?	no
Tests pass?	yes
Fixed tickets	#166, #167
License	MIT
Doc PR

[baspeeters]

🔔 @dunglas, @sroze, @theofidry, @soyuka

[dunglas]

Thanks @baspeeters!